A well may be utilized to form a fluid connection between a subterranean formation that includes a reservoir fluid and a surface region. The well may include a wellbore, or hole, that extends between the surface region and the subterranean formation, and the wellbore may contain, or be lined with, a wellbore casing that defines a casing conduit. Prior to beginning production, or conveyance, of reservoir fluid from the subterranean formation through the casing conduit to the surface region, one or more well completion operations may be performed to place the well in condition for production and/or to improve, or increase, a potential rate of wellbore fluid production therefrom.
Well completion operations often utilize a perforation device to form perforations within the wellbore casing. Subsequent to formation of the perforations, a stimulant fluid, such as a fracturing fluid and/or an acid, may be provided from the casing conduit, through the perforations, and to a portion of the subterranean formation that is proximal thereto. This stimulant fluid may alter the characteristics of the portion of the subterranean formation, thereby increasing a production rate of reservoir fluid from the well.
Often, it is desirable to fluidly isolate one or more selected perforations that are present within the wellbore casing from a remainder of the perforations that may be present within the wellbore casing to provide for more controlled delivery of the stimulant fluid to a selected portion of the subterranean formation that is proximal to the one or more selected perforations. Traditionally, this isolation has been accomplished by inserting a setting tool into the casing conduit to set a plug at a location within the casing conduit that is uphole from the perforations that are currently present within the casing conduit, which may fluidly isolate an uphole portion of the casing conduit from the perforations that are currently present within the casing conduit. Subsequent to setting the plug, a perforation device may be introduced into the casing conduit to create the one or more selected perforations at a location that is uphole from the plug.
The perforation device is then removed from the casing conduit, and the stimulant fluid may then be provided to a region of the casing conduit that is uphole from the one or more selected perforations. The plug directs the stimulant fluid through the one or more selected perforations and into the portion of the subterranean formation that is proximal thereto. The process may be repeated any suitable number of times to create any suitable number of perforations and stimulate any suitable number of portions of the subterranean formation.
While the above procedure may be effective at stimulating a plurality of portions of the subterranean formation, the process of inserting and/or positioning the various pieces of equipment into and/or within the casing conduit and subsequently removing the various pieces of equipment from the casing conduit prior to inserting and/or positioning the next piece of equipment into and/or within the casing conduit may increase the overall cost of the well completion operation, as well as the time required thereby. In addition, and after stimulation of a desired number of zones of the subterranean formation, the casing conduit will include a plurality of plugs that must be removed therefrom prior to production of reservoir fluids from an entire length of the well. It follows that removal of these plugs contributes additional time and expense to the well completion operation.
More recently, well completion operations have been developed that may decrease a number of plugs that may be needed for the completion operation, that may perforate and selectively stimulate a plurality of zones of the subterranean formation without removal of the perforation device from the casing conduit, and/or that may utilize other processes to temporarily fluidly isolate, or decrease fluid flow through, at least a portion of the plurality of perforations. For example, diversion agents, such as ball sealers, have been utilized to temporarily decrease fluid flow through one or more selected perforations. These diversion agents may be introduced into the casing conduit from the surface region while the perforation device is present within the casing conduit and may flow down the casing conduit with the stimulant fluid. Ideally, the stimulant fluid will direct the diversion agents toward the one or more selected perforations and provide for contact and sealing therebetween.
While such a system may be effective at decreasing fluid flow through a perforation, the sealing between the diversion agents and the perforations is often imperfect and/or may degrade over time. In addition, the distance between the surface region and the one or more selected perforations may be on the order of thousands, or even tens of thousands, of feet. Thus, the time required to pump the diversion agents from the surface region to the one or more selected perforations may be significant, or at least difficult to predict with certainty. Furthermore, the diversion agents may tend to disperse along the length of the casing conduit, making it difficult to provide the diversion agents to the one or more selected perforations at a target, or desired, concentration and/or increasing a potential for failure of the diversion agents to effectively seal a portion of the one or more selected perforations. In addition, the pumping and/or completion equipment may limit the types and/or sizes of diversion agents that may be provided to the casing conduit.
For example, conventionally, the diversion agents must flow from, or proximate, the surface region and past the perforation device that is downhole in the casing conduit in order to reach the one or more selected perforations. Additionally, the diversion agents must be introduced into the casing conduit while the casing conduit is under pressure, and the diversion agents typically must travel a long distance within the casing conduit prior to reaching the one or more selected perforations. Furthermore, processes that utilize diversion agents often may form and seal a limited number of perforations before a leakage rate through the perforations becomes significant relative to a flow rate of stimulant fluid into the casing conduit, thereby decreasing the flow rate of stimulant fluid into a target zone of the subterranean formation. In order to decrease and/or stop this leakage, packers or plugs may once again be utilized to fluidly isolate respective portions of the casing conduit, and these packers or plugs also must be removed from the casing conduit prior to production from the entire well. Thus, there exists a need for improved systems and methods for secondary sealing of perforations in a wellbore casing.